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Chapter 5. Diet and Water Requirements: Important Southwestern Deer Foods
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Chapter 5 Diet and Water Requirements Important Southwestern Deer Foods A ny discussion of deer diets must begin with a look at the main food items. Pictured in this section are a few important plants in the diet of southwestern deer (Figs. 27–38). Deer Diets Kufield et al. (1973) summarized 99 studies of mule deer diet and reported that 788 different species of plants were eaten by mule deer. Despite the abundance of diet studies throughout the country on whitetails and mule deer, it is still difficult to make generalized statements about what plants deer eat. The species composition of plants consumed by deer varies tremendously by geographical area, elevation, season, and year. Some shrubs that are relished by deer do not appear in any deer diet studies simply because no studies were conducted where those plants were common. Obviously, deer living in different vegetation associations will not eat the same proportions of the same plant species. Mule deer in southern Colorado could not have the same diet as those in Sonora, Mexico. Fluctuating climatic conditions and the resulting effect on the vegetation causes major differences in plant growth and nutritional quality. With this in mind, it is evident that one short-term study on “what deer eat” could not possibly describe the complicated fluctuations in deer diets. Some stud- 98 chapter 5 ies were conducted during a time when deer were nutritionally stressed, so the most prevalent food items consumed may be those available at the time, rather than the types of food deer prefer. In addition, studies have been conducted using very different methods to determine which foods are important to deer—for example , examining rumen contents or fecal pellet contents, watching wild or tame deer eat, and feeding tame deer different plants. All this complicates our ability to compare different studies. Even studies using the same methods may report the results in different ways. For example, some data are presented as the percentage of sampled deer that ate each plant species, while other studies reported the percentage of the stomach contents that a particular plant amounted to. In spite of these limitations, however, looking at the major deer foods reported in the more significant studies allows us to piece together a picture of which plants are the most nutritionally important to southwestern deer. Mule Deer Through the annual, seasonal, and elevational changes in diet, deer rely heavily on browse for much of the year (Table 6). Although mule deer use browse species heavily in most seasons, it is especially important during times of less rainfall. Depending on precipitation and temperature, diets shift heavily in favor of forbs (broad-leaved weeds) when they become available following the summer or winter rainfall periods. In the Chihuahuan Desert, a higher percentage of the annual rainfall occurs in the summer; the resulting summer forb growth is a more signi ficant factor for mule deer in that part of the Southwest. Cactus and shrub/ tree fruits are always used intensively where and when they occur in abundance. Most deer studies have shown that grass makes up a very small portion of deer diets , usually being important only for a short time when it is the first vegetation to green up in the spring. Other plants, such as mistletoe, can make important contributions to a deer’s diet. Mistletoe is known to be relished by deer, so we should not be surprised to learn that it is high in carbohydrates and is easily digestible (Urness 1969). Mistletoe is not normally high in protein, but one of the desert varieties (Phoradendron californicum) can run as high as 15–25 percent protein. The first organized study on deer diets in the Southwest was the pioneering work by A. A. Nichol (1938), one of the first research projects conducted with the new Wildlife Restoration Funds derived from the Pittman-Robertson Act of 1937 (see Table 3). Nichol assembled a collection of seven mule deer from the Kaibab Plateau and one from southwestern Arizona, and held them in captivity on the Santa Rita Experimental Range south of Tucson. Throughout the study, these deer were fed 168 different native plant species to determine which ones they considered palatable. By measuring how much of each plant species the deer consumed, Nichol developed a list of the plants deer preferred. This was a step in the right direction , but the diet of deer in the wild is dependent on what plants are available [3.235.145...